BritGrav 15

Live tweets from the 15th British Gravity Meeting, University of Birmingham

  1. First session (Chair: Christopher Berry)

  2. First up, Chris Collins talks is about testing gravity with the Inverse Square Law experiment. #BritGrav15
  3. Haoyu Wang talks about talks about reducing thermal noise in Advanced LIGO #BritGrav15
  4. Josh Freedman on his masters' project modelling laser beam modes for Advanced LIGO #BritGrav15
  5. Duncan Meacher on a mock data challenge for the Einstein Telescope, a future gravitational-wave detector. #BritGrav15
  6. Meacher: ET detections out to max of z ~ 2. #BritGrav15
  7. Yiming Hu explains how we can be confident that we have actually made a gravitational-wave detection. #BritGrav15
  8. Hu: estimating noise background noise in LIGO difficult as we can't shield detectors from signals. Need network of detectors. #BritGrav15
  9. Alex Nielsen on detecting neutron star-black hole binaries with Advanced LIGO #BritGrav15

  10. Session 2 (Chair: Miranda Bradshaw)

  11. Christopher Berry @cplberry talks about binary neutron stars measurements with Advanced LIGO #BritGrav15
  12. .@cplberry Chirp mass measured well even without spin. Sky area hundreds of square degrees 
  13. Will Vousden @willvousden on speeding up parameter estimation with parallel tempering of MCMC: use a dynamical chain #BritGrav15
  14. .@willvousden: Dynamical chain gives a factor of a few improvement  In process of testing for LIGO data. #BritGrav15
  15. Chris Moore on how to overcome uncertainty in waveform templates for Advanced LIGO parameter estimation. #BritGrav15
  16. Moore: Need to understand effects of noise AND waveform uncertainty. Marginalise out waveform uncertainty using Gaussian process regression!
  17. Jade Poxwell @JadePowell12 on using gravitational waves to learn about supernovae collapse #BritGrav15
  18. .@JadePowell12 Uncertainty in supernovae waveforms. New paper on results this summer! #BritGrav15
  19. @BritGrav15 I'm not looking at uncertainty in the waveforms just using them to find explosion mechanism :-)
  20. Simon Stevenson @simon4nine talks about understanding the astrophysics of binaries: important for understanding gravitational waves
  21. Distinguishing population synthesis models using gravitational waves  by @simon4nine, Ohme & Fairhurst
  22. #Britgrav15 is off to a good start - 'black hole spin alignments' Simon Stevenson
    #Britgrav15 is off to a good start - 'black hole spin alignments' Simon Stevenson
  23. .@simon4nine Including spin precession of black holes adds info to waveform. It is an imprint of binary evolution #BritGrav15
  24. Could you tell direct collapse black holes from those via neutron star collapse? @simon4nine: Maybe via natal kick. #BritGrav15
  25. Hannah Middleton on using pulsar timing arrays to detect background of background gravitational waves from massive black holes #BritGrav15
  26. We need an array of pulsars to detect a stochastic gravitational wave background - Hannah Middleton #britgrav15
    We need an array of pulsars to detect a stochastic gravitational wave background - Hannah Middleton #britgrav15
  27. Middleton: What can a PTA upper limit tells us about black hole population? Not much about anything other than number density. #BritGrav15
  28. Middleton: Detection is more constraining! Frequency dependence could help constrain more physics. #BritGrav15

  29. Session 3 (Chair: Hannah Middleton)

  30. Davide Gerosa on the most massive black holes in the Universe. Increase by a factor of 2 in mass since z = 2 by mergers #BritGrav15
  31. Gerosa: Undermassive BHs in BCGs indicates a larger number of mergers. A missing BH means a superkick from merger 
  32. Maggie Lieu @Space_Mog on weak lensing mass measurement of galaxy clusters, a useful probe for cosmology #BritGrav15
  33. .@Space_Mog: Use hierarchical modelling to describe population! Thanks @farrwill. Few assumptions & can include selection effects.
  34. Mateja Gosenca on general relativistic N-body simulations. Important for testing GR or including relativistic perturbations #BritGrav15
  35. Gosenca: Assume spherical symmetry to build intuition, relax this in the future.
  36. Viraj Sanghai on constricting a post-Newtonian cosmological models #BritGrav15
  37. Gregory Ashton on periodic variability (timing noise) in pulsars. Precession or beam switching? #BritGrav15
  38. Ashton: Using spin-down data and cool Bayesian methods... can't tell if it's precession or beam switching. Need beam width data too!
  39. Vanessa Graber on the magnetic fields of neutron stars. Magnetars have fields of 10^15 G! #BritGrav15
  40. Graber: What happens if we consider superconductivity (type II)? Hexagonal array of quantized flux tubes!
  41. Graber: Need to consider vortex-flux tube interactions to get larger friction and shorter evolution timescale. #BritGrav15
  42. Graber: Large number of flux tubes (10^18 cm^-2) allows averaging for macroscopic properties. #BritGrav15
  43. Alice Harpole discusses type I X-ray bursts: explosive fusion in ocean of accreted material on neutron star #BritGrav15
  44. Harpole: Strong-gravity effects likely to be important, need to include in simulations. Can use low-Mach approximation #BritGrav15
  45. Konstantinos Palapanidis on the inside of neutron stars. Strong interaction between proton and neutron fluids. #BritGrav15

  46. Session 4 (Chair: Maggie Lieu)

  47. Nigel Martin on interpreting the relationship between the Einstein and Weyl tensors.
  48. Jarrod Williams on the constant equations for numerical relativity calculations. These describe initial conditions #BritGrav15
  49. Gernot Heißel also on initial data. Current codes use wormhole data for black holes. These evolve to trumpets: start there! #BritGrav15
  50. Heißel: Presenting numerical derivation for Schwarzschild trumpet data as a guideline for Kerr. Matches analytical solution. #BritGrav15
  51. Heißel: Hopefully have Kerr initial trumpet data for next BritGrav! #BritGrav16
  52. William Cook on gravitational waves in higher dimensions. Simulations done in 5D. Building on that with new formalism. #BritGrav15
  53. Sebastian Khan on new gravitational waveform with inspiral, merger and ringdown plus precession! #BritGrav15
  54. Khan: PhenomD is frequency domain (fast). Calibrated against more waveforms. All matches better than 0.98! #BritGrav15
  55. Khan: PhenomD beats SEOBNR for large spins and high mass ratio. #BritGrav15

  56. Session 5 (Chair: Chris Collins)

  57. To start off, Tedora Oniga on gravitational decoherence, which is still not well understood. #BritGrav15
  58. Spurgeon Talaganis on understanding loops in higher derivative gravity #BritGrav15
  59. Talaganis: Non-local gravity has novel features, might be worth further study!
  60. Lisa Glaser on Hartle Hawking wave function in causal set quantum gravity. A lot for 10 min, she's going to speak quickly! #BritGrav15
  61. Jos Gibbons is talking about massless scalar fields, which he promises are really relevant for a gravitational conference #BritGrav15
  62. Gibbons: de Sitter space is interesting because of symmetry and because the universe is falling up (accelerating) #LittleBritGrav
  63. Gibbons: More details in our paper  Still working on gravity calculations #BritGrav15
  64. Ilia Musco will give us the latest results regarding quasi-static solutions for compact objects in Chameleon models #BritGrav15
  65. Musco: Chameleon mechanism screens scalar fields so it can explain dark energy and evade local measurements. #BritGrav15
  66. Musco: Universal solution for incompressible star, central scalar field depends on compactness M/R and coupling strength #BritGrav15
  67. Colombo: Horava sacrifices Lorentz invariance for renormalization. This analysis gives 4th-order dispersion relation, which could risk this!
  68. Aindriú Conroy explains the Raychaudhuri equation before what it means to be geodesic incomplete. #BritGrav15

  69. Session 6 (Chair: Will Farr)

  70. Christian Luebbe on conformal cyclic cosmologies (CCC). He'll be using conformal scalar fields. #BritGrav15
  71. Luebbe: Can use conformal scalar field (CSF) to map aeons. Does CSF control inflation? Are there applications in AdS/CFT? #BritGrav15
  72. Alex Leithes talking on coupled quintessence. Replace cosmological constant to remove coincidence problem. Developing code to test theory.
  73. Leithes: For 1st time, evolution of stable perturbations in 2 fluid, 2 field, sum of exps model. Papers for PYESSENCE soon #BritGrav15
  74. Adam Christopherson @AJChristo is interested in axions, a potential candidate for dark matter. #BritGrav15
  75. .@AJChristo: Modelling axion as a classical field with Schroedinger-Poisson equations. This reproduces homogeneous background. #BritGrav15
  76. .@AJChristo: Need inhomogeneities for structure formation. Linear Newtonian perturbations reproduced from Schroedinger-Poisson equations!
  77. Linear Newtonian perturbation theory from the Schrödinger-Poisson equations by Banik @AJChristo Sikivie & Todarello 
  78. Brien Nolan is going to tell us about his favourite spacetime: McVittie (embedding of Schwarzschild in FRW) #BritGrav15
  79. Nolan: Looking at a black hole in an expanding Universe. First looking at Class 2: no cosmological constant. Singular boundary at r = 2m.
  80. Nolan: Class 1, with cosmological constant: can extend across r = 2m to Schwarzschild-de Sitter. More like a black hole! #BritGrav15
  81. Nolan: Does black hole or expansion win? Depends where you are, stable orbits are possible. #BritGrav15
  82. Matthew Wright on a solution for slowly rotating perfect fluids with a cosmological constant  #BritGrav15
  83. Wright: Can't match slowly rotating solution to asymptotic flat space, trying de Sitter. This works (up to 2nd order in angular velocity).
  84. Edgar Gasperín on conformal geometry. Analysing extremal Swarzschild-de Sitter #BritGrav15
  85. Michael Cole will be telling us about Killing spinors. Killing spinors tell us about properites (Petrov type) of spacetime #BritGrav15
  86. Cole: In electrovacuum, trying to find Killing spinor. Could evolve integrability condition with suitable initial conditions #BritGrav15

  87. Session 7 (Chair: Simon Stevenson)

  88. David Dempsey on the bound states of the Dirac equation in Kerr  A black hole hydrogen atom #BritGrav15
  89. Dempsey: Tested analytic results and found new features at critical frequency. Next, looking at hyperfine structure. #BritGrav15
  90. Dempsey: Tested analytic results and found new features at critical frequency. Next, looking at hyperfine structure. #BritGrav15
  91. Vladimir Toussaint on a particle detector in a cylindrical spacetime where there is no privileged vacuum state. #BritGrav15
  92. Toussaint: Simplest detector: a 2-level quantum system. Can distinguish two spin structures by zero mode. #BritGrav15
  93. Benito Juárez-Aubry is going to talk about quantum effects at a Cauchy Horizon, but not Gandalf. #BritGrav15
  94. Juárez-Aubry: Respect causality and don't do near a Cauchy horizon! #BritGrav15
  95. Hugo Ferreira wants to calculate local observables for a rotating black hole background (using a quasi-Euclidean method). #BritGrav15
  96. Supakchai Ponglertsakul is looking at black hole solutions in Einstein-charged scalar field theory. #BritGrav15
  97. Ponglertsakul: Kerr surrounded by mirror: super-radiant instability can lead to a black hole bomb.
  98. Ponglertsakul: What could be the end point of instabilities? Hairy black holes found numerically. These seem stable. #BritGrav15
  99. Yafet Sánchez Sánchez: general relativity predicts its own breakdown through the presence of singularities. #BritGrav15
  100. Sánchez Sánchez: Singularities are obstructions to dynamics of test fields. Wave regularity is a useful tool.
  101. Bernard Kay on black holes in a box (not an astrophysical black hole… ) #BritGrav15
  102. Umberto Lupo also thinking about black holes in a box  Is there a description of thermal equilibrium? #BritGrav15
  103. Lupo: Looking for sufficiently regular free Klein-Gordon field. Still a few loose ends, but it doesn't look like it exists in toy case.

  104. Session 8 (Chair: Alberto Vecchio)

  105. Timothy Clifton introduces IOP Gravitational Physics Group thesis prize. £500 prize AND the chance to present at BritGrav!
  106. 2014 Thesis Prize Winner Anna Heffernan
  107. First @PhysicsNews prize talk: Anna Heffernan, The Self-Force Problem #BritGrav15
  108. Heffernan: Self-force is useful for extreme mass-ratio systems. Models back-reaction of smaller object's mass on larger mass' spacetime.
  109. Heffernan: Some overlap between post-Newtonian perturbation theory and self-force. Self-force has been used to determine PN coefficients
  110. Heffernan: Need self-force for extreme mass-ratio inspirals (EMRIs), a gravitational-wave source for eLISA! See 
  111. Heffernan: EMRIs provide detailed map of background (Kerr) spacetime, probe galactic centres and so galaxy formation, black holes, etc.
  112. Heffernan: Need to calculate field; need to remove singular part. Start with scalar field, then electromagnetic, then gravitational.
  113. Heffernan: Singular field doesn't look nice when written down, but makes some pretty plots! (Slide 28: )
  114. Heffernan: Need to be careful subtracted infinities. Will use mode-sum regularization with cunning coordinate choice. #BritGrav15
  115. Heffernan: Using this improvement in self-force calculations, others went on to investigate ISCO, etc. #BritGrav15
  116. Heffernan: Then went on to Kerr to make life difficult! We also looked at non-geodesic motion. Self-force maintains a similar form.
  117. Heffernan: Looked at effective source method as alternative to mode-sum. More pretty pictures on slide 56 ( )
  118. Heffernan: No EMRI waveforms as yet. Need more accurate Kerr results, 2nd order terms and orbit evolution. #BritGrav15
  119. Heffernan: Lots of thesis highlights. It went well! [Applause] #BritGrav15
  120. Dolan: Recent work on identifying gauge-invariant quantities instead of going directly for waveforms. #BritGrav15
  121. 2015 Thesis Prize Winner Patricia Schmidt
  122. This year's winner Patricia Schmidt: Modelling Precessing Black Hole Binaries. #BritGrav15
  123. Patricia Schmidt gives the second GPG thesis prize talk of the day. @BritGrav15
    Patricia Schmidt gives the second GPG thesis prize talk of the day. @BritGrav15
  124. Interview with Patricia Schmidt, 2015 GPG thesis prize winner  via @PublisherAD
  125. Schmidt: Want inspiral-merger-ringdown (IMR) waveforms for detection and parameter estimation in advanced detection era. #BritGrav15
  126. Schmidt: Astrophysical binaries have arbitrary spin configurations. Spin misalignment introduces precession. Lots of interesting effects!
  127. Schmidt: For aligned spins, everything evolves in a plane, nice and simple! Well understood and well modelled (e.g. EOBNR)
  128. Schmidt: With arbitrary precession, everything changes! We see this directly in the gravitational waveform. Amplitude and phase changes.
  129. Schmidt: Tracking of orbital plane difficult in GR: use direction of dominant emission direction. #BritGrav15
  130. Schmidt: Quadrupole aligned (QA) waveforms closely resemble spin-aligned waveforms. QA waveforms aren't physical, but this is intriguing!
  131. Schmidt: Use QA mapping to identify precessing and aligned-spin waveforms. This identifies single effective spin parameter.
  132. Schmidt: Considered 17 precessing configurations & mass ratios 3, 10. Best waveform matches > 0.99. QA waveforms do agree well!
  133. Schmidt: Have removed precession! Now use inverse procedure to make precessing waveforms: do the twist! #BritGrav15
  134. Schmidt: Do we need to consider ALL physical parameters to describe precession dynamics? Leading order: precession from S orthogonal to L.
  135. Schmidt: Over many precession cycles, can use average of spin. Checking match shows reduced spin parameters work. #BritGrav15
  136. What about the spin precession? Schmidt: Hard to disentangle from residual eccentricity. Both effects are small.
  137. Are we limited by lack of numerical waveforms to check against? Schmidt: Parameter space is huge. Work being done to explore. #BritGrav15
  138. Best Student Talk Prize
  139. #BritGrav15 best student talk prize sponsored by #CQG… Runners up Viraj Sanghai & Umberto Lupo. Winner: Christopher Moore! Congratulations!
  140. Thanks to John Miller, Carsten Gundlach & John @JohnVeitch for judging, and for @PublisherAD for the prize! #BritGrav15
  141. Public lecture